Heat exchanger having plural tubular arrays

ABSTRACT

A heat exchange apparatus including a housing, a first array of fluid conduits provided within the housing, and a second array of fluid conduits provided within the housing. The first and second arrays of fluid conduits are configured to carry a first fluid. The heat exchange apparatus also includes a first fluid passageway provided within the housing, where the first fluid passageway is defined by an internal surface of the housing and by a baffle plate. The first fluid passageway is configured to carry a second fluid. The baffle plate is configured to divide the first fluid passageway into a first flow path and a second flow path, where the first array of fluid conduits extends through the first flow path and the second array of fluid conduits extends through the second flow path.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional Application of U.S. Ser. No.10/791,746, filed Mar. 4, 2004, which is hereby incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to heat exchangers and methodsof constructing heat exchangers.

2. Discussion of the Background

Heat exchangers and heat exchange chemical reactors having large arraysof parallel tubes are known in the art. Traditional design practices forsuch articles are codified in design standards. U.S. Pat. No. 6,497,856(the '856 patent), which is hereby incorporated by reference, teaches aheat exchange chemical reactor for producing hydrogen from natural gas,propane, liquefied petroleum gas (LPG), alcohols, naphtha and otherhydrocarbon fuels. Typical industrial applications include feedstock forammonia synthesis and other chemical processes, in the metals processingindustry, for semiconductor manufacture and in other industrialapplications, petroleum desulfurization, and hydrogen production for themerchant gas market. The demand for low-cost hydrogen at a smaller scalethan produced by traditional industrial hydrogen generators has createda market for small-scale hydrogen production apparatus (<15,000 standardcubic feet per hour (scfh)). This demand has been augmented by thegrowing enthusiasm for hydrogen as a fuel for stationary and mobilepowerplants, especially those employing electrochemical fuel cells,which require hydrogen as a fuel.

U.S. application Ser. No. 10/436,060 (the '060 application), filed onMay 13, 2003, which is incorporated herein by reference, discloses anadvantageous heat exchange apparatus that provides a cost-effective heatexchange structure that reduces shell-side fluid leakage and bypass fortubular heat exchangers such as those operated at high temperatures andpressures. FIG. 1 of the '060 application shows a tubular heat exchangercore including an array of tubes 2, which are sealingly connectedbetween a first tubesheet 3 and a second tubesheet 4. A first fluidflows from an inlet manifold sealingly attached to the first tubesheet3, through tubes of the array of tubes 2, and out a second manifoldattached to the second tubesheet 4. The array of tubes 2 is provided onouter surfaces of the tubes with flow directing baffles or plates 5,which are used to cause a second fluid to flow substantially normal tothe axis of the array of tubes 2. All of the baffles have a smallextended portion 18, which extends outside the flow passageways andfinned zones in each fluid stage. The extended portions 18 are providedfor mating to refractory ductwork for directing the flow of the secondfluid. FIG. 2 of the '060 application shows a structure that providesimproved manifolding of the flow within a housing 100 formed by housingmembers, such as sheet cover pans 20, 30 and portions of various bafflesthat form part of the outer shell of the heat exchanger, such asportions of baffles 13-16 and 19. The housing 100 can achieve acondition of zero leakage.

However, the inventors of the present invention have determined that theheat exchange apparatus described in the '060 application has certaincapacity restrictions that are improved in the present invention.Thermal stress management is one of the largest, if not the largest,limiting factor in the reformer technology described in the '856 patentand the '060 application. Since the reformers tend to operate under highthermal stress, as the reactor is scaled up in size, a high pressuredrop (i.e., change in pressure, ΔP) across the tube array can put largestresses on the baffles and the pan ductwork. These large stresses leadto premature failure due to creep at services temperatures. The pressuredrop can be lowered by simply increasing the cross sectional area of theheat exchanger stages with attendant larger pan areas, however, thestresses are far greater in larger pans for the same pressure load.Thus, simply increasing the heat exchanger stage area does not providean adequate solution. Additionally, when the reactor is scaled up insize, the overhanging burner box is plagued by high stresses, due to thelarge size of the pans and due to the cantilever forces from the burner.Furthermore, very big reactors require very thick tubesheets. Thesethick, beefy tubesheets are not only expensive, but they are also veryrigid. Thus, large offset holes are required in the tubesheets in orderto prevent the thermal expansion of the tubesheets from damaging thearray of tubes extending therethrough, although such holes can beminimized as discussed in U.S. Pub. No. 2003/0173062 A1, which is herebyincorporated in its entirety by reference. Such large through-holeslimit the effectiveness of the reformer by causing bypassing of the tubearrays.

It is therefore desirable to provide a heat exchange structure thatovercomes the capacity restrictions discussed above.

In the manufacture of hydrogen, and especially in the manufacture ofhydrogen according to the process of U.S. Pat. No. 6,623,719 (the '719patent) wherein the combustion air is preheated in the cooling of thewater gas shift process, the simultaneous control of the flametemperature, water gas shift process temperature and steam reformerinlet temperatures can be extremely difficult. Departure from thepreferred temperature conditions can cause poor fuel conversion, highthermal stresses, excessive corrosion, and problems with localcondensing and reboiling of steam within the system. These deficienciesare particularly problematic during transient operation, such asstartup, shutdown and load changes. It is therefore desirable to provideapparatus for and a method of controlling undesirable departures fromthe preferred operating temperatures.

In the '719 patent, some thermal energy is lost to the ambient as wasteheat after the water gas shift process in the process condenser. Thiswasted heat energy undesirably increases the operating cost of thehydrogen process and increases emissions of climate change gases. It istherefore desirable to provide apparatus for and a method of recoveringadditional waste heat that is economical to build and does not adverselyimpact the operability of the hydrogen generating process.

SUMMARY OF THE INVENTION

The present invention advantageously provides a heat exchange apparatusincluding a housing having a first fluid passageway provided therein.The first fluid passageway is defined by an internal surface of thehousing and by a baffle plate. The first fluid passageway is configuredto carry a second fluid. A first array of fluid conduits and a secondarray of fluid conduits are provided within the housing. The first arrayof fluid conduits and the second array of fluid conduits are configuredto carry a first fluid. The baffle plate is configured to divide thefirst fluid passageway into a first flow path and a second flow path,and the first array of fluid conduits extends through the first flowpath and the second array of fluid conduits extends through the secondflow path.

The present invention also advantageously provides a bottom moduleincluding the housing and first fluid passageway, and a top modulehaving an additional fluid passageway extending therethrough andincluding a superheater section, a boiler section, and a preheatersection. The top and bottom module and the fluid passageways thereinhave a vertical arrangement that advantageously utilizes buoyancy ofheated fluid flowing through the passageways in order to create anatural draft through the top and bottom modules, thereby reducingpressure inside the heat exchanger. Ideally, a vacuum is attained insidethe reformer housing. This effect can also be supplemented with theaddition of an exhaust fan.

The present invention also provides an air diverting means and a methodof use to facilitate accurate dynamic control of the processtemperatures during all operating modes. The present invention alsoprovides a heat recovery air preheater that may be closelymechanically-integrated into the reactor of the present invention or thereactor of the '856 patent facilitate improved heat recovery whencompared to the process of the '719 patent. A method of operating theimproved heat recovery means either independently, or more preferably inconjunction with the air diverting means is also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will become readily apparent with reference to thefollowing detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

FIG. 1 depicts a front, cross-sectional view of a first embodiment of aheat exchanger of the present invention;

FIG. 2A depicts a side view of the top and bottom modules of the heatexchanger of FIG. 1;

FIG. 2B depicts a side view of an alternative embodiment of the heatexchanger;

FIG. 3A depicts a schematic view of a container for a top module of thepresent invention;

FIG. 3B depicts a schematic view of a container for a bottom module ofthe present invention;

FIG. 4 depicts a front, cross-sectional view of a second embodiment of aheat exchanger of the present invention;

FIG. 5 depicts an enlarged cross-sectional view of a portion of the zoneof reinforced tubes from FIG. 1;

FIG. 6 depicts an enlarged cross-sectional view of an array of tubeshaving heat fins; and

FIG. 7 depicts a cross-sectional view of the housing of the bottommodule of the heat exchanger with various layers of insulation and shellcasings.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described hereinafter withreference to the accompanying drawings. In the following description,the constituent elements having substantially the same function andarrangement are denoted by the same reference numerals, and repetitivedescriptions will be made only when necessary.

FIG. 1 shows a heat exchanger 10 including a bottom module 20 having afirst tubular heat exchanger core 30 and a second tubular heat exchangercore 40. The first core 30 includes an array of substantially-parallelconduits or tubes 32, which are sealingly connected between a firsttubesheet 50 and a second tubesheet 60. The second core 40 includes anarray of substantially-parallel conduits or tubes 42, which aresealingly connected between the first tubesheet 50 and the secondtubesheet 60. A first fluid flows from one of a plurality of inletmanifolds 51 provided adjacent to the first tubesheet 50, through tubesof the array of tubes 32 and the array of tubes 42, and out of one of aplurality of second manifolds 61 provided adjacent to the secondtubesheet 60. The manifolds 51 and 61 are shown in FIG. 2A as connectedto manifold pipes 52 and 62, however, alternatively the manifolds can beone or more chambers sealingly attached to the respective tubesheets. Inthe present embodiment of the invention, one or more rows of tubes ofthe array of tubes 32, 42 can be attached to a single inlet manifold 51and/or a single outlet manifold 61. For example, two rows of tubes inthe array of tubes 32 can be fluidly connected to a single inletmanifold pipe 51 and a single outlet manifold pipe 61.

The tube arrays 32 and 42 are provided on outer surfaces of the tubeswith flow directing baffles or plates 34, 36, which are used to cause asecond fluid to flow substantially normal to the axis of the tube arrays32 and 42. One or more baffles 34, 36 may be provided to produce severalconsecutive stages of cross-flow of the second fluid across the array oftubes, which conveys the first fluid. The baffles 34, 36 are configuredto provide a serpentine flow of second fluid through the bottom module20. The baffles 34 extend across the central portion of the bottommodule 20 and provide flow gaps 35 at outer sides of the bottom module20. The baffles 36 are configured such that two baffles 36 are providedat the same elevation within the bottom module 20 such that the twobaffles 36 extend inward from the sides of the bottom module 20 andprovide a central flow gap 37. Thus, the second fluid is directed tosplit in two directions to flow around baffle 34 and through flow gaps36 and then rejoin at a central portion and flow though the central flowgap, as indicated by the flow arrows in FIG. 1. The baffles 34, 36 inFIG. 1 are of a preferred rectangular planform. The tubular arrays 32,42 of FIG. 1 are likewise rectangular, although the present invention isin no way limited to tubular arrays and baffles having a rectangularplanform, and can be provided with any planform desired.

The bottom module includes lower flow passages 80 that extend from aninlet 110 to an outlet 120, and upper flow passages 90 that extend froman inlet 140 to an outlet 150. In the lower flow passages 80, the flowof second fluid enters through inlet 110, which is located in a centralportion between the tubular arrays 32, 34. The baffle 34 causes thesecond fluid within the lower flow passages 80 to divide such that afirst flow path 82 is created around one side of the baffle 34 and asecond flow path 84 is created around the other side of the baffle. Theportion of the second fluid that travels along the first flow path 82 isdirected through the tubular array 32, and the portion of the secondfluid that travels along the second flow path 84 is directed through thetubular array 34. The portion of the second fluid that travels along thefirst flow path 82 and the portion of the second fluid that travelsalong the second flow path 84 join at the central location and exitthrough outlet 120. In the upper flow passages 90, the flow of secondfluid enters through inlet 140, which is located in a central portionbetween the tubular arrays 32, 34. The baffle 34 causes the second fluidwithin the upper flow passages 90 to divide such that a first flow path92 is created around one side of the baffle 34 and a second flow path 94is created around the other side of the baffle. The portion of thesecond fluid that travels along the first flow path 92 is directedthrough the tubular array 32, and the portion of the second fluid thattravels along the second flow path 94 is directed through the tubulararray 34. The portion of the second fluid that travels along the firstflow path 92 and the portion of the second fluid that travels along thesecond flow path 94 join at the central location where they travelupward through gap 37 to the next level, where the flow split isrepeated.

FIG. 1 depicts a heat exchanger core configured to provide the flowarrangement of the '856 patent, which is incorporated herein in itsentirety. The baffles 34, 36 can be arranged to execute any sort of flowpattern desired, such as a simple counterflow or parallel flow heatexchange. In the flow arrangement depicted in FIG. 1, the flow of thesecond fluid is divided into two separate flow passageways by a sealingzone 70. In FIG. 1, a sealing method of refractory felt gaskets isemployed in the sealing zone 70 between the lower flow passages 80 andthe upper flow passages 90. The second fluid may flow through both ofthese passages after some intermediate processing, such as adding fuelto the second fluid including air and burning the resultant mixture, ora distinct third fluid may flow in one of the passages. In either case,it is likely that the fluid pressure of the streams in flow passages 80and 90 will be different, and thus a pressure gradient will exist acrossthe sealing zone 70.

It should also be noted that heat exchange fins 33, 43 may beadvantageously placed on outer surfaces of the tubes in the tubulararrays 32, 42 to increase heat transfer area, protect against corrosion,and provide mechanical support to the tubes. The heat exchange fins canbe plates that extend across all of the tubes of the tubular array 32and plates that extend across all of the tubes of the tubular array 42,or the fins can consist of strip-like plates (or “banked fins”) 700 thatextend across all of the tubes in a one or more rows of tubes of thetube arrays 32, 42, as depicted in FIGS. 1 and 6. The strip-like plates700 are preferred for situations where thermal gradients across thecross-flow stage are sufficiently high to impose deleterious mechanicalstress on the tubes 42. In situations where thermal stresses are notdamaging, a greater number of tube rows are preferably encompassed in asingle fin to reduce assembly time and expense for the heat exchanger.In the embodiment depicted in FIG. 1, the rows of tubes in the tubearrays 32, 42 are each connected to a single tube 51 (which can also bereferred to as a tubular inlet manifold) at the top of the bottom module20 and all of the tubes 51 are then connected to the inlet manifold 52,and the rows of tubes in the tube arrays 32, 42 are each connected to asingle tube 61 (which can also be referred to as a tubular outletmanifold) at the bottom of the bottom module 20 and all of the tubes 61are then connected to the outlet manifold 62. Since each row of tubes inthe tube arrays 32, 42 are each connected to individual tubes 51, 61,then, for thermal expansion reasons, it is preferred to utilizestrip-like plates 700 for the heat transfer fins in order to reduce anystress on the inlet manifold 52 and the outlet manifold 62 by theindividual tubes 51, 61. When compared to the rigid tube sheets of the'856 patent, which imposes differential thermal expansion stresses intwo axes in the plane of the tubesheet, the manifolds 51, 61 of thepresent invention advantageously exert differential expansion stressesin only one axis. Thus, the methods for reducing the effects of thermalexpansion described in U.S. Pub. No. 2003/0173062 A1 may beadvantageously employed with a reduced amount of flow bypassing. Theimportance of this advantage increases as the physical size of the heatexchanger increases.

One feature apparent in FIG. 1 is the various sizes of the baffleplates. Baffle plates 34, 36 prevent flow of the second fluid parallelto the tubes, while permitting flow in this direction through the gaps35, 37. Full baffle plates 72, 74 are provided on either side of thesealing zone 70 and prevent any flow of the second fluid parallel to thetube arrays 32, 42. All of the baffle plates 34, 36, 72, 74 depicted inFIG. 1 are formed with a small extended portion 38 (the extendedportions of baffle plates 34 are not shown in FIG. 1, but extend alongthe front and rear sides of the housing 100), which extends outside theflow passageways and finned zones in each fluid stage where the baffleplate adjoins and is mounted to the housing members. The extendedportions 38 are provided for mating to refractory insulation and forproviding a thermal expansion means for the ductwork structure as perthe method of the '060 application.

FIGS. 1 and 2A depicts a housing 100 formed by housing members, such assheet cover pans 102. The housing 100 of the present invention canachieve a condition of zero leakage. The housing 100 is constructed bycreated flange joints at the locations where adjacent edges of the coverpans 102 are joined. Flange joints are also formed at locations whereextended portions 38 of the baffles 34, 36 are sandwiched between edgesof adjacent cover pans 102. Flange joints 104 can be made essentiallyfluid impermeable by methods such as welding, brazing, adhesive bonding,roll forming or other methods apparent to one of ordinary skill in theart. It is particularly advantageous to weld or roll-form the flangejoints at the joints between of the edges of the cover pans and thebaffles 34, 36, such that the flanged edges of the cover pans mayelastically-deflect under differential thermal expansion to relievestresses on the assembly and prevent permanent deformation of thebaffle, the pans, or both. This embodiment of the present inventionadvantageously accommodates elastic deflections both parallel andperpendicular to the tube arrays.

In an alternative embodiment of the present invention, one or more ofthe cover pans 102 may be attached by bolts, screws, or other removablefixing devices. In such an embodiment it is preferable to provide astationary sealing member in between the adjacent cover pans 102, andbetween the cover pans 102 and the extended portion 38 of the baffleplates 34, 36. An advantage of this alternate embodiment is that thecover pans may be removed to inspect and/or clean the heat exchangercore including the heat exchange arrays 32, 34. This feature ishighly-desirable under some heat exchanger service conditions, wherecorrosion or deposition of fouling are expected to be high.

The cover pans 102 of the present invention may be made of any materialcompatible with the operating conditions. It is, however, preferred toconstruct the baffle pans from metal sheet stock. The flange featuresare then very easily formed using typical sheet metal processing, andthe fluid joints can be readily made.

FIG. 2A shows the heat exchanger 10 of FIG. 1 outfitted with a burner130 provided between an outlet 120 of the lower flow passages 80 and theinlet 140 of the upper flow passages 90. The lower flow passages 80 havean inlet 110, which introduces the second fluid into the heat exchanger,and the upper flow passages 90 have an outlet 150, which discharges thesecond fluid into the top module 200. The heat exchanger 10 canoptionally include an air preheater 160 that heats the second fluidprior to the inlet 110 using the heated first fluid from the secondmanifold 62. In this optional embodiment, the second fluid enters a coldcombustion air inlet 170 and can travel either to the air preheater 160along passage 172 and then to the inlet 110, or the second fluid cantravel from the cold combustion air inlet 170 along passage 174 directlyto the burner 130. The flow of the second fluid along passages 172, 174is controlled by valves 180, which can be, for example, proportionalbutterfly valves controlled by actuator configured to drive a controllinkage 182 connected to both valves 180 or individual actuatorsconfigured to control the valves 180 independently. The valves 180control the temperature of the second fluid exiting the outlet 120 ofthe lower flow passages 80 and the temperature of the second fluidentering the burner 130. In an alternative embodiment, the two valvesmay be replaced with a single valve that continuously modulates flowbetween the passages 172, 174, such valves are known in the art andreferred to variously as diverter or selector valves. In anotheralternative embodiment, one passage may be provided with a continuouslymodulating valve while the other passage is provided with no valve. Inthis embodiment, pressure losses in the system are advantageouslyreduced but the range of flow variation is disadvantageously decreased.This alternative embodiment may be preferred in situations where only asmall dynamic range of flow ratios between the two passages is desired.

In one embodiment of the present invention the heat exchanger 10 isemployed for the production of hydrogen, and the tubes 32 and 42 areprovided with appropriate catalysts as disclosed in the '856 patent. Inthis embodiment, the first fluid exits the zone corresponding to thelower flow passages 80 of the bottom module 20 after undergoing acatalytic, non-isothermal water gas shift reaction as described in the'856 patent as well as in the '719 patent, which is hereby incorporatedby reference in its entirety. Both the '856 patent and the '719 patentteach that the first fluid may be further reacted in a water gas shiftreactor operating under essentially-adiabatic conditions. In the '856patent, this reactor may optionally be appended to the tube sheet at theexit of the zone corresponding to the lower flow passages 80. However,the rigid tube sheet of the '856 patent undesirably imparts thermalstresses to the heat exchanger, reducing its service life oralternatively requiring extensive measures to mitigate the effects ofthe thermal mismatch in the heat exchanger. It is advantageous toprovide a separate reaction vessel for the execution of the water gasshift reaction subsequent to the exit of the first fluid from themanifold pipe 62. Reactor vessels and attendant connections suitable forthis purpose are known to those of ordinary skill in the art.

Subsequent to the further water gas shift reaction which is desirablyexecuted according to the methods of the '856 and '719 patents, thefirst fluid retains a great deal of sensible heat and latent heatassociated with the condensation of steam. If this heat is recovered bythe second fluid, it desirably reduces the fuel consumption required togenerate hydrogen according to the '856 and '719 patents. Provision ofan air preheater may thus achieve this reduction in fuel use, and isdesirable when fuel costs are high or when emissions of byproduct gasessuch as CO₂ are undesirable.

The embodiment of FIG. 2A advantageously allows for independent controlof the amount of heat recovered from the first fluid and the temperatureof at least one other point. For instance, in the case of a hydrogengenerator wherein the second fluid is combustion air, the flowrate ofthe air may be modulated to achieve a desired temperature of the firstfluid exiting the zone corresponding to the lower fluid passages 80through the manifold pipe. This degree of control may advantageouslyallow the fine adjustment of reaction conditions in the subsequent watergas shift reactor. Thus, the reactor's operating characteristics may beoptimized to yield the smallest size, greatest hydrogen production,lowest methanation rate, etc. By simultaneously varying the flowrate offuel to the burner 130, the flame temperature at the inlet 140 to theupper steam reforming zone corresponding to the upper flow passages 90may also be controlled. This advantageously permits close control of themaximum temperature experienced by the tubes 32, 42, thus permittingincreased life of the heat exchanger.

Further control of temperatures may be advantageously obtained byselecting the heat transfer capacity of the various heat exchangeelements. Thus, the temperature of the mixed burner inlet air to theburner 130 may be modulated below the maximum permissible limit for theburner assembly. The temperature of the mixed steam and fuel in theinlet manifold 52 to the steam reforming zone corresponding to the upperflow passages 90 may also be modulated to optimize performance accordingto the teachings of the '856 and '719 patents. This may be achievedwhile also maintaining the flame temperature at inlet 140, the water gasshift temperature and, by proper heat exchanger design, the temperatureof the burner inlet air. This degree of process control permits muchgreater operational stability of a hydrogen generator employing thevalves 180, and may be advantageously employed whether or not an airpreheater is used. The control valves 180 thus provide a surprisingability for a hydrogen generator of the present invention to be operatedat conditions other than the full design flowrates without significantdeviations from the preferred process conditions, such as thoseenunciated in the '856 and '719 patents. Further, the modulating valvesand air preheater of the present invention may be advantageouslyemployed with related art steam reformers and water gas shift reactorswithout limitation.

In another embodiment of the present invention, a hydrogen generatoremploying the modulating valves 180 and the air preheater 160 isdesigned such that the amount of heat transferred between the first andsecond fluids in the air preheater is not sufficient to causesignificant condensation of the water vapor in the first fluid. Thisembodiment is preferred in situations where the flashing of condensedwater when removed from the system in a water separator is undesirable.This may be due to objectionable noise generated by the phasetransition, by increased wear on the valve used to void the condensedwater, or due to concerns of corrosion or valve durability in handlingthe high temperature condensed water. It may also be desirable to limitthe heat transfer to eliminate condensing under conditions where theattendant burner air inlet temperature would exceed the permissiblelimits. Thus, although the greater heat transfer in a condensing airpreheater may be preferred where savings in fuel usage are a determiningfactor, other situations may make the employment of a non-condensingpreheater more desirable. The characteristics of the heat transfersurfaces of the air preheater and the heat exchanger zone correspondingto the lower flow passages 80 may be selected to achieve the desiredheat flux using techniques known to one of ordinary skill in the art.

FIG. 2B depicts an alternative embodiment of the heat exchanger. Theembodiment depicted in FIG. 2B is identical to the embodiment of FIG.2A, except that the alternative embodiment does not include the airpreheater 160, the cold combustion air inlet 170, and valves 180 of FIG.2A, but rather a simplified connection to inlet 110 and a simplifiedconnection between the outlet 120 and the burner 130 via passage 122.

The modulating valves of the present invention provide especialadvantage in operation of a hydrogen plant during startup, shutdown andidle. During startup, the alternate embodiment 2B must supply all burnerair through the simplified conduits. This airflow removes an undesirablyhigh amount of heat from the first fluid, which would otherwise be usedto increase the temperature of the zone corresponding to the lower flowpassages 80 and the subsequent water gas shift reactor. This heatremoval may cause extensive condensation within the first fluidpassages. This condensation may undesirably impede flow of the firstfluid. It may also cause physical or chemical damage to the catalystsdisposed within the tubes 32, 42 and the subsequent water gas shiftreactor, if used. Thus, in a preferred embodiment of the presentinvention, a hydrogen plant provided with modulating valves 180 maysubstantially-reduce second fluid flow through the zone corresponding tothe lower flow passages 80, thus decreasing cooling of the first fluid,diminishing condensation, and reducing the time required for startup.

During shutdown and idle, the modulating valves may be employed much asabove to regulate the temperatures of the first fluid. Depending uponthe system operating details, shutoff and idle conditions may presentrisks of undesirable high or low temperatures. Further, undesirablebackflow to the second fluid supply may also occur. By proper use of themodulating valves, these conditions may be completely avoided. Apreferred method of operating the plant in a transition from a hydrogenproducing mode of operation to a hot idle operation is to use the valves180 to block flow through the upper passage 174, while permitting flowthrough passage 172. The supply of air through the inlet 170 is alsoterminated. In this state, the buoyancy of the heated air betweenpassage 172 and 174 will not cause an undesirable movement of heat tothe valve or attached piping. Instead, the static pressure differencebetween the passage 172 and the preheater 240 will cause any airflow tomove from the passage 172 to the preheater without unduly heating valves180.

All of the figures have illustrated cover panels covering an entire sideof a polygonal tube array with one panel. In some applications, theservice pressure and temperature combined with the dimension of the heatexchange core make it desirable to provide a number of sub-panels on oneor more sides. This advantageously reduces the mechanical stresses for agiven cover plate thickness and provides additional thermal expansionjoints. Thus, the number and thickness of cover plates provided in agiven location may be varied to suit the local temperature and stressconditions.

FIG. 1 depicts the heat exchanger sealing zone 70 of the presentinvention. The sealing zone 70 is defined by baffle plates 72 and 74.The sealing zone 70 includes refractory felt seals 78 and one or morelayers of intumescent material 76. It is likely that a pressuredifferential will exist between the lower flow passage 80 and the upperflow passage 90, and thus the refractory felt seals 78 reduce leakageand thermal stresses.

The present invention preferably includes the sealing zone 70, which isespecially useful when the fluid entering the upper flow passage 90 isat a temperature above a service limit for intumescent material of 800°C. and the fluid exiting the lower flow passage 80 is below the servicelimit for the intumescent material. In this embodiment, the gap betweenthe baffle plates 72 and 74 is filled with one or more layers ofrefractory material, such as refractory felt gaskets 78, cast withmoldable refractory fiber, or stuffed with loose refractory fibers. Therefractory material is in intimate contact with the baffle 74, which isin contact with the upper flow passage 90. This refractory material isinitially installed in sealing contact with the tubes of the tube arrays32, 42, the baffle 74, and the internal surface of the housing 100. Oneor more layers of intumescent material 76 are then provided between therefractory material 78 and the baffle 72. The intumescent material 76 isseparated from the upper flow passage 90 by sufficient refractory 78,which acts as a thermal insulator to prevent overheating of theintumescent material 76. The two baffles are held in essentially fixedmechanical relationship by mechanical means such as connection to bafflesupport rods as known in the art, by mechanical capture between layersof extended heat exchange fins in intimate contact with the tubes 32,42, or by other means apparent to one of ordinary skill in the art.

Upon heating above 300° C., the intumescent material 76 expands normalto the face of the baffles 72, 74. This expansion subjects therefractory 78 to substantial pressure. Under this pressure, therefractory 78 is compressed to a higher density than when it wasinstalled. Further, the refractory 78 is forced by this pressure intoimproved sealing contact with the tubes of the tube arrays 32, 42 andinternal surface of the housing 100. Because the cover plates of thehousing 100 are essentially fixed, the expansion of the intumescentmaterial 76 in a direction parallel to the tubes is thus converted intoa uniform pressure to the refractory felt material 78.

The choice of thickness of the refractory material 78 and the quantityof intumescent material 76 is dictated by the desired compression of therefractory 78 in question, the refractory's anticipated shrinkage inservice, the expansion characteristics of the intumescent material 76,and the mechanical strength of the baffles, pans (housing) and theirmechanical supports. Thus, many different combinations are possiblewhich may be uniquely suited to the exact type of heat exchangeranticipated and its operating conditions.

The especially preferred intumescent mat products are formulated toresist erosion by flowing heated gas. Thus, a captured intumescent sealof the present invention is inherently resistant to failure by erosion.

The outlet 150 of the upper flow passage 90 of the bottom module 20 isconnected to a manifold section 210 of a top module 200 provided abovethe bottom module 20. The outlet 150 is preferably connected to themanifold section 210 by a slip joint 202 or by other means which providefluid sealing and accommodate thermal expansion differences and isreadily connected at the installation site, e.g., fabric or metalbellows. The manifold section 210 depicted in FIGS. 1 and 2A includesinclined side walls 212 and an inclined front wall 214. This inclinationis dictated by the dimensions of the components employed, and is notintended to limit the invention in any way.

The second fluid exiting the outlet 150 enters the manifold section 210and then travels through a superheater 220, through a boiler section230, and through a preheater section 240, and then exits the top module200. The top module 200 utilizes heat from the heated second fluidexiting the bottom module, in order to heat the first fluid before thefirst fluid enters the inlet manifold 52. The top module 200 is orientedin a vertical manner in order to take advantage of the natural buoyancyof the heated second fluid, however, an optional exhaust fan 250 can beprovided at the exit 242 of the top module 200 in order to create aforced draft and reduce pressure within the bottom module 20. Thus, avacuum can be attained within the bottom module 20 with regard to thesecond fluid.

The first fluid enters the top module 200 as a liquid via a pipe 244that extends through the preheater section 240. The first fluid absorbsheat from the second fluid in the preheater section 240, and thentravels via a pipe 246 to a boiler 232 in the boiler section 230. Thefirst fluid is transformed from a liquid to a gas in the boiler 232 byabsorbing heat from the second fluid in the boiler section 230. Thegaseous first fluid then travels via a pipe 234 to the superheatersection 220, where the first fluid travels along a pipe 222 that makesseveral passes through the superheater section 220. The first fluid thentravels from the superheater section 220 via a pipe 224 to the inletmanifold 52. One or more additional fluids may be introduced at anypoint in the process. These fluids may be liquids, or gases. In oneembodiment of the present invention, the additional fluid is ahydrocarbon feedstock for the production of hydrogen.

FIGS. 3A and 3B depict schematic views of containers for the top module200 and the bottom module 20 of the present invention. The containersare used as a means for efficiently shipping and assembling the heatexchanger 10 of the present invention. A container 300 is provided forthe top module 200, in which the top module 200 is housed within thecontainer 300 at the manufacturing plant and shipped in the container300 to the assembly site. Similarly, a container 400 is provided for thebottom module 20, in which the bottom module 20 is housed within thecontainer 400 at the manufacturing plant and shipped in the container400 to the assembly site. When the containers 300, 400 arrive at theassembly site, then the bottom module container 400 is positioned in theappropriate final location, and then the top module container 300 isstacked on top of the bottom module container 400. Preferably, analignment or mounting feature, such as the mounting feature 410schematically shown in FIG. 3B, is provided the top module container 300and/or the bottom module container 400. By stacking the top modulecontainer 300 on the bottom module container 400, the top module 200will be joined to the bottom module 20 by the slip joint 202. Althoughnot depicted, the exhaust fan 250 could also be housed within a shippingand assembly container that can be used to easily ship and assemble theexhaust fan 250 to the top of the top module 200.

FIG. 4 depicts a second embodiment of the present invention in which themanifold section has been modified to accommodate two outlets 152 fromthe upper flow passage of the bottom module. In the embodiment depictedin FIG. 4, the number of cross-flow stages in the upper flow passage hasbeen changed such that the flow exiting the bottom module is travelingout from the sides, rather than from the centrally located outlet 150depicted in FIG. 1. The manifold section 500 depicted in FIG. 4 hasgenerally vertical side walls 152, but the inclination of the walls willbe dictated by the relative dimensions of the components, and is notlimiting. The manifold section 500 is preferably connected to the bottommodule by slip joints 502 or by some other means which can accommodatevertical thermal expansion differences and is readily connected at theinstallation site.

In the embodiment depicted in FIGS. 1 and 4, the area of the heatexchanger adjacent to the inlet 140 to the upper flow passages 90 is thehottest portion within the heat exchanger. In this hot area, it ispreferable to provide a zone of reinforced tubes 600. FIG. 5 depicts anenlarged cross-sectional view of a portion of the zone of reinforcedtubes 600 from FIG. 1. In the zone of reinforced tubes 600, the tubes inboth the first tube array 32 and the second tube array 42 are providedwith an outer sleeve 602 that adds strength to the tubes of the tubearrays 32, 42 within this hot zone where creep stress might otherwisecause the failure of the tubes. This supporting sleeve advantageouslydoes not transmit shear stress between the tubes 32, 42 and the sleeve,thus reducing the total stresses in the heat exchanger. It alsoadvantageously reduces the material usage required to sustain a highermetal temperature. It also advantageously allows the use of a differentmaterial for the tubes and the support sleeve. Thus, a material withenhanced resistance to degradation under the second fluid conditions maybe selected for the support sleeve while a material optimized for thefirst fluid conditions may be selected for the tubes themselves.

In the present application it is preferred to increase (as compared tothe process described in the '856 patent) the flame temperature of theburner to a range of between 1050° C. and 1250° C. in order to allow forthe reduction the flowrate of the second fluid without a drop in heattransfer to the first fluid. By reducing the flowrate of the secondfluid, the pressure drop through the heat exchanger is advantageouslyreduced. When the temperature of the fluid is so high, then heattransfer is almost all radiant, and thus heat transfer fins (whichincrease pressure drop) are not necessary. Thus, no heat transfer finsare depicted in the zone of reinforced tubes 600 of the preferredembodiments of the present invention. The use of reinforcing outersleeves 602 is preferred when the temperature of the second fluid isabove about 900° C., and more preferably above 1000° C. The reinforcingouter sleeves 602 can be positioned on the outer surface of the tubes ofthe tube arrays 32, 42 using force fitting methods, rapid hydraulic ormechanical expansion methods, or other methods that produce a tight fitbetween the outer surface of the tube and the inner surface of thereinforcing outer sleeve.

FIG. 7 depicts a cross-sectional view of the housing of the bottommodule 20 of the heat exchanger with various layers of insulation andshell casings. The present invention includes a first layer ofinsulation formed of a plurality of blocks of insulating refractoryboard 800. The blocks of refractory board 800 can be temporarilyattached to the outer surface of the cover pans 102 by an adhesive 802,for example, masking tape. The blocks of refractory board 800 areattached to the outer surface of the cover pans 102 such that the entireor substantially the entire outer surface of the housing 100 is coveredwith the refractory boards 800. The adhesive 802 is intended to hold therefractory boards 800 in position until a first casing 810 is mounted onthe outer surface of the refractory boards 800 and the housing 100. Thefirst casing 810 holds the refractory boards 800 in place. The firstcasing is preferably made of plural panels of galvanized sheet metalthat are joined together using fasteners.

As depicted in FIG. 7, the present invention also includes a secondlayer of insulation formed of a plurality of blocks of insulatingrefractory board 820. The blocks of refractory board 820 are preferablylarger than the blocks of refractory board 800 in the first layer ofinsulation and preferably overlap with the blocks of refractory board800 in the first layer such that any gaps between the boards 800 arecovered by boards 820. The blocks of refractory board 820 can betemporarily attached to the outer surface of the first casing 810 by anadhesive 822, for example, masking tape. The blocks of refractory board820 are attached to the outer surface of the first casing 810 such thatthe entire or substantially the entire outer surface of the first casing810 is covered with the refractory boards 820. The adhesive 822 isintended to hold the refractory boards 820 in position until a secondcasing 830 is mounted on the outer surface of the refractory boards 820and the housing 100. The second casing 830 holds the refractory boards820 in place. The second casing is preferably made of plural panels ofgalvanized sheet metal that are joined together using fasteners.

In an alternative preferred embodiment, the present invention includesone or more layers of insulation with a single shell casing. Forexample, the present invention preferably includes a first layer ofinsulation formed of a plurality of blocks of insulating refractoryboard that are temporarily attached to the outer surface of the coverpans 102 by an adhesive. The blocks of refractory board are attached tothe outer surface of the cover pans 102 such that the entire orsubstantially the entire outer surface of the housing 100 is coveredwith the refractory boards. Additionally, a second layer of insulationformed of a plurality of blocks of insulating refractory board isprovided on an outer surface of the first layer of insulation using anadhesive such that the blocks of the second layer preferably overlapwith the blocks of refractory board in the first layer. Additionallayers of insulation can be provided as needed, for example an outermostlayer of glass fiber matting or a layer of high performance insulationsuch as mesoporous silica or alumina. Then an outer casing is mounted onthe outer surface of the outermost layer of insulation in order to holdthe insulation in place.

The present invention splits the reactor into n=2 or greater independenttube bundles. The embodiment depicted in FIGS. 1 and 2A showconfigurations having two tube bundles 32, 42, however the presentinvention contemplates embodiments having more than two bundles wherethe second fluid flow is fed by common inlets and share common outlets.By increasing the number of independent bundles to a number greater thanone, the present invention reduces the velocity of the second fluidflowing through a given tube bundle by 1/n. The reduction in velocity ofthe second fluid flow through a given bundle reduces the pressure dropof the second fluid in the bottom module by between 50% and 75%. Thepresent invention also eliminates the overhanging burner box from the'060 application by creating a burner box in the middle of the two cores32, 42, adjacent to the inlet 140. The flame is fully developed in thetube leading from the burner 130 to the inlet 140, which can be isolatedby one or more elastic members (e.g., bellows) 132 in order to divorcethe burner weight from the reactor. The burner 130 can be rigidlymounted to a supporting frame.

The present invention advantageously utilizes buoyancy of the heatedsecond fluid in order to create a natural draft through thereformer/bottom module 20, superheater section 220, boiler section 230,and preheater section 240, plus optional forced daft from the exhaustventilation fan 250, in order to reduce pressure inside the reformer.Ideally, a vacuum is attained inside the reformer housing. This effectis enhanced by the vertical arrangement of elements as depicted in orderto get a greater “chimney height.”

It should be noted that the exemplary embodiments depicted and describedherein set forth the preferred embodiments of the present invention, andare not meant to limit the scope of the claims hereto in any way.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A method for producing hydrogen, comprising the step of: feeding atleast one fuel into a reactor comprising a housing having an inlet andan outlet, and a flow path extending within the housing from the inletto the outlet, the flow path comprising a convectively-heated catalyticsteam reformer and a convectively-cooled water gas shift reactor,whereby hydrogen is produced, wherein a burner is provided to heat thesteam reformer, wherein combustor product from said burner is modulatedby a flow diverting mechanism to maintain a predetermined operatingtemperature of the steam reformer, wherein the combustion air is used tocool the water gas shift reactor before the combustion air is providedto the burner, and wherein the combustion gas is preheated prior tobeing used to cool the water gas shift reactor, and wherein thecombustion gas is preheated to a temperature whereby the combustion gasis provided to the burner at a predetermined temperature that is notgreater than an allowable burner inlet temperature.
 2. A method forproducing hydrogen, comprising the step of: feeding at least one fuelinto a reactor comprising a housing having an inlet and an outlet, and aflow path extending within the housing from the inlet to the outlet, theflow path comprising a convectively-heated catalytic steam reformer anda convectively-cooled water gas shift reactor, whereby hydrogen isproduced, wherein a burner is provided to heat the steam reformer,wherein combustor product from said burner is modulated by a flowdiverting mechanism to maintain a predetermined operating temperature ofthe steam reformer, and wherein a flow passage used to carry thecombustion air from an inlet of the housing to an outlet of the housingis vertically configured to allow combustion gas to exit the outlet dueto buoyancy properties of heat air.
 3. The method according to claim 2,wherein the flow passage is configured to allow combustion gas to exitthe outlet due to buoyancy properties of air even when the inlet isclosed.
 4. A method for producing hydrogen, comprising the step of:feeding at least one fuel into a reactor comprising a housing having aninlet and an outlet, and a flow path extending within the housing fromthe inlet to the outlet, the flow path comprising a convectively-heatedcatalytic steam reformer and a convectively-cooled water gas shiftreactor, whereby hydrogen is produced, wherein fluid used toconvectively heat the steam reformer and convectively cool the water gasshift reactor is modulated by a flow diverting mechanism to maintain thesteam reformer at a temperature above which water can condense therein.5. A method for producing hydrogen, comprising the steps of: feeding atleast one fuel into a reactor comprising a housing having an inlet andan outlet, and a flow path extending within the housing from the inletto the outlet, the flow path comprising a convectively-heated catalyticsteam reformer and a convectively-cooled water gas shift reactor,whereby hydrogen is produced; and minimizing an amount of cooling fluidused to cool the water gas shift reactor using a modulating valve tocontrol the flow of the cooling fluid.
 6. The method according to claim5, wherein said cooling fluid is combustion air that is provided to aburner to heat the steam reformer.
 7. A method for producing hydrogen,comprising the step of: feeding at least one fuel into a reactorcomprising a housing having an inlet and an outlet, and a flow pathextending within the housing from the inlet to the outlet, the flow pathcomprising a convectively-heated catalytic steam reformer and aconvectively-cooled water gas shift reactor, whereby hydrogen isproduced, wherein a burner is provided to heat the steam reformer,wherein a temperature of combustion product from said burner iscontrolled by controlling a total flowrate of combustion air to theburner, and wherein an amount of cooling fluid used to cool the watergas shift reactor is controlled using a modulating valve to control atemperature of the water gas shift reactor.
 8. The method according toclaim 7, wherein said cooling fluid is combustion air that is providedto the burner.